Spinal cord stimulation (SCS) has emerged as a promising therapy for treating chronic, intractable pain in individuals refractory to kinetic (e.g., rehabilitation), pharmaceutical, and surgical therapies. For example, across 74 studies looking at 3,025 individuals with chronic leg and back pain, 58% of the patients reported greater than 50% reduction in pain following SCS. However, despite its success, current SCS devices are still prone to failures; the three most common being poor pain coverage, lead migration, and lead breakage. Poor pain coverage and small lead misplacements can sometimes be overcome by reprogramming the stimulation parameters, but large lead misplacements and lead breakage require an additional surgery to reposition or replace the lead. These revision surgeries are costly, as they add additional expenses (e.g., time off work and additional stimulator hardware), and they obligate the patient to incur risks associated with the surgery. Therefore, there are still opportunities for improving SCS, such as lead design.
Typical SCS devices include an implantable pulse generator (IPG) placed subcutaneously in the buttock or abdomen and a set of wires connecting the IPG to an array of stimulation electrodes placed in the epidural space of the spinal canal. Currently, there are two types of array designs: percutaneous arrays of 4-8 cylindrical electrodes on a cylindrical substrate and surgical (i.e., paddle) arrays of 4-20 rectangular/disk electrodes on a planar substrate, both of which are implanted parallel to the long axis of the spine. Arrays are advantageous because each contact can be programmed individually, making outcomes less sensitive to anatomical variations and differences in electrode placement, but with increasing number of electrodes, programming becomes a challenge.
Computational modelling can be useful tool for SCS device design. Modeling studies have shown that percutaneous arrays in longitudinal (rostral-caudal) bipolar and tripolar configurations, and paddle arrays in transverse (medial-lateral) tripolar configurations, outperform monopolar configurations in selective activation of the targets of SCS, the dorsal column (DC) fibers, over the undesirable targets, the dorsal root (DR) fibers. However, other than a couple of studies looking at optimal electrode geometry and spacing for a longitudinal bipolar and tripolar configuration; lead design, lead placement, and selection of stimulation parameters has been largely a trial and error process. Trial and error experimentation is not an efficient approach and is unlikely to lead to an optimal result, as the efficacy of SCS depends on the geometry, polarity, and location of the stimulation electrodes. Although there have been advances in SCS, there is a continuing need for improved techniques and systems for optimizing SCS.